Many millable frac and bridge plugs utilize nonmetallic components to facilitate ease of milling during plug removal. Of the nonmetallic materials used, commonly filament and convolute-wound composites are used. These wound materials have high hoop strengths, making them well suited for cylindrical, load-bearing components such as cones and mandrels.
In conventional systems, filament and convolute-wound composites are made by winding around a solid wrapping mandrel. The filament or sheet is coated with resin prior to application onto the wrapping mandrel and successively layered until the desired dimensions are achieved. Once the part is complete, it is cured and the wrapping mandrel is removed. The resulting part is extremely strong, relatively cheap, and quick to manufacture.
Due to the manufacturing process required to make these wound components, parts with solid inner diameters cannot be made. This is generally not an issue for frac plugs where flow area through the inner diameter (“ID”) is desired. However, most bridge plugs have functional requirements that necessitate a solid ID. As a result, corks or other mechanical components are installed in wound mandrels for bridge plugs to obstruct their IDs and allow them to act as “solid” components. Unfortunately, these corks may be problematic both in manufacturing, installation, and operation.
Therefore, there is a need for an improved wound composite mandrel to improve manufacturing and installation, and to facilitate milling operations.